1. Field of the Invention
The present invention relates to a magnetic tape to be used advantageously particularly for recording computer data. More specifically, it relates to a magnetic tape to be used advantageously particularly in a magnetic recording and reproduction system using an MR head (MR head for recording a signal with a 10 to 100 Mbit/cm2 surface recording density).
2. Description of the Related Art
Recently, a system with a thin film magnetic head assembled has been used practically in a magnetic recording and reproduction system for recording and reproducing computer data. Since the thin film magnetic head can be processed easily for miniaturization or into a multi track head, a multi track fixed head of a thin film magnetic head has been used frequently particularly in a system using a magnetic tape as the recording medium. By use of the thin film magnetic head, improvement of the track density and improvement of the recording efficiency can be achieved owing to the miniaturization so as to realize high density recording as well as improvement of the data transfer rate can be enabled owing to achievement of the multi track. The thin film magnetic head can be classified to an induction type head responding to the time change of a magnetic flux, and a magnetic resistance type head (MR head) utilizing the magnetic resistance effect responding to the size of a magnetic flux on the whole. Since the induction type head has a small head coil winding number due to the flat structure, it involves the problem of difficulty in enlarging the magnetomotive force so that a sufficient reproduced output cannot be obtained. Therefore, an MR head capable of easily obtaining a high reproduced output is used for the reproduction, and in contrast, an induced type head is used for the recording. These recording and reproduction heads are assembled in a system ordinarily as an integrated type (composite type). In the above-mentioned magnetic recording system, a linear recording method capable of realizing a higher data transfer is adopted.
As a magnetic tape for recording computer data used for a magnetic recording and reproduction system with the MR head assembled, for example, magnetic tapes corresponding to the 3480 type, the 3490 type, the 3590 type, and the 3570 type of the IBM standard are known. These magnetic tapes have a basic structure comprising a relatively thick magnetic layer including a ferromagnetic powder and a binder, with a 2.0 to 3.0 xcexcm thickness in a single layer structure provided on a support. These magnetic tapes comprising a single layer structure magnetic layer involves a problem in that it cannot sufficiently satisfy the recent need as a medium for storing a large number of data.
In order to deal with the problem, as a magnetic recording medium used in a magnetic recording system with a thin film magnetic head assembled, for example, JP-A-8-227517 discloses a magnetic recording medium (magnetic tape) comprising a lower non-magnetic layer with an inorganic non-magnetic powder dispersed in a binder provided on a non-magnetic support, and a thin upper magnetic-layer with a ferromagnetic metal powder dispersed in a binder provided on the non-magnetic layer. Since the output decline due to the thickness loss can be restrained as well as a high recording density can be achieved by making the upper magnetic layer thinner (0.3 xcexcm), storage of data can be enabled with a larger capacity compared with a magnetic tape comprising a single layer structure magnetic layer. Moreover, JP-A-11-250449 similarly discloses a magnetic tape comprising a magnetic layer on a non-magnetic layer.
In a magnetic recording and reproduction system adopting a linear recording method, the track width for recording and reproduction in a magnetic tape tends to be narrower in order to realize a larger recording capacity with a higher recording density. At the time or recording and reproduction, the magnetic head moves in the magnetic tape width direction (vertical direction) and either track should be selected. With a narrower track with, a higher accuracy is required for controlling the relative position of the magnetic tape and the head.
The conventional linear recording method is designed such that the magnetic tape running position is fixed by a guide or the like so that the head can be moved in the vertical direction at a predetermined position. However, with a narrower track width, since the reproduction head runs off the optimum position with the data recorded in the case the tape is stretched due to the influence by change of the environment, such as the temperature and the humidity, or the tape running position is displaced from the anticipated running position, the output can easily be lowered. Therefore, recently, a method of recording a servo signal in the longitudinal direction of a magnetic head, detecting the relative position of a head with respect to the tape by the servo signal, and controlling the head position so that the head can run at the optimum position of a track, is utilized. The servo signal includes a plurality of servo bands, and has a signal changeable in the width direction in each servo band. Therefore, by reproducing the servo signal, the position of the reproduction head can be detected with respect to the servo band. In a system utilizing a magnetic tape with such a servo signal recorded, it is preferable that the interval between the servo bands in the width direction, and the servo band width are not changeable. That is, it is preferable that the size in the width direction of the magnetic tape is not changeable.
In contrast, since the magnetic tape for the above-mentioned system is used by high speed running and repeated running, unchangeability of the size in the longitudinal direction thereof is required increasingly than before because the tensile force of the magnetic tape tends to be larger in the system in order to ensure the contact of the magnetic tape with respect to the MR head (contact state with respect to the MR head) in a system using an MR head capable of high density recording. In particular, the tensile force is increased at the time of stoppage or running in the BOT part (the starting end part of the tape wound around on a tape reel) and the EOT part (the finishing end part of the tape wound around on the tape reel) of the magnetic tape. As a result, the magnetic tape can be stretched so as to cause the output decline, or thereby, the size of the magnetic tape in the width direction is influenced particularly in the magnetic tape with the servo signal recorded as mentioned above so that the track control is disturbed so as to easily generate an error. Therefore, in the magnetic tape for the above-mentioned system, a dynamical strength higher than the conventional one is desired in the longitudinal direction thereof.
Moreover, a higher magnetic tape output is preferable in order to achieve high density recording.
According to the discussion of the present inventors, it was found that further improvement is required in terms of the tracking characteristic and the other tape running characteristics for utilizing the magnetic tape disclosed in JP-A-8-227517 for the above-mentioned system. That is, it was found out that the magnetic tape has a relatively large change in the width direction with respect to the temperature or humidity change, and thus in the case of recording or reproduction using the tape, the tracking accuracy is deteriorated so that a sufficient reproduction output can hardly be obtained even in the case the track control is executed by the servo signal, or an error can easily be generated after repeated running.
Furthermore, according to the magnetic tape disclosed in JP-A-11-250449, a sufficient high output reproduction cannot be obtained in the case of high density recording, and thus improvement has been called for.
An object of the invention is to provide a magnetic tape having a high recording density suitable for a magnetic recording and reproduction system utilizing a linear recording method, with an MR head assembled. In particular, it is to provide a magnetic tape having a high recording density and the excellent durability, with little change of the size of the magnetic tape width direction, capable of recording and reproducing repeatedly with a high output and a high reliability by reducing the track displacement (off track) at the time of running even in the case of a track with a narrow width.
By the further study of the inventor, it was found out that the stable tracking characteristic can be obtained with little off track at the time of running even in the case of a narrow width track by restraining the temperature and humidity expansion coefficients in the width direction of the magnetic tape, and reinforcing the dynamical strength in the tape longitudinal direction so as to reduce the size change particularly in the tape width direction in a magnetic tape for recording a signal with a 10 to 100 Mbit/cm2 surface recording density. Moreover, a magnetic tape with the excellent durability, capable of obtaining a sufficient recording and reproduction characteristic can be provided even in the case of recording a signal of a 10 to 100 Mbit/cm2 surface recording density by having a 1.0 nm or less center plane average roughness (SRa) of the support on the magnetic layer coating surface side, a 3.0 to 9.0 nm center plane average roughness (SRa) of the support on the opposite surface, and 10 pieces/100 cm2 or less projections of a 273 nm or more height existing on the magnetic layer coating a surface side.
The invention provides a magnetic tape comprising a non-magnetic layer containing a non-magnetic powder and a binder, which is substantially non-magnetic, and a magnetic layer containing a ferromagnetic powder and a binder on one surface of a support in this order, and a back coating layer containing a carbon black on the other surface of the support, wherein the magnetic tape is a magnetic tape for recording a signal with a 10 to 100 Mbit/cm2surface recording density, having a 0.0015%/xc2x0 C. or less temperature expansion coefficient in the width direction of the magnetic tape, a 0.0015%/% RH or less humidity expansion coefficient, a 10 N or more offset yield strength in the longitudinal direction of the magnetic tape, a 30N or more rupture strength, a 1.0 nm or less center plane average roughness of the support on the magnetic layer coating surface side, a 3.0 to 9.0 nm center plane average roughness of the support on the opposite surface, and 10 pieces/100 cm2 or less projections of a 273 nm or more height existing on the magnetic layer coating surface side of the support.
A magnetic tape of the invention preferably has the following embodiments.
(1) The support is made of a polyethylene naphthalate.
(2) The center plane average roughness of the support on the magnetic layer coating surface side is 1.0 nm or less.
(3) The center plane average roughness of the support on the back coating layer coating surface side is 9.0 nm or less (further preferably 5 nm or less).
(4) Projections of a 273 nm or more height exist on the magnetic layer coating surface side of the support by 10 pieces/100 cm2 or less (further preferably 5 pieces/100 cm2 or less).
(5) The magnetic tape width is in the range of 5 to 13 mm (further preferably 7 to 13 mm, particularly preferably 10 to 13 mm).
(6) The magnetic tape entire thickness is in the range of 5 to 10 xcexcm (further preferably 7 to 9.5 xcexcm, particularly preferably 7.5 to 9.5 xcexcm).
(7) A servo signal is recorded along the magnetic tape longitudinal direction for controlling the relative position of the recording and reproduction heads with respect to the magnetic tape in the width direction.
(8) The above-mentioned magnetic tape is for a magnetic recording and reproduction system using an MR head.
(9) The above-mentioned magnetic tape is for recording computer data.